Optical coherence tomography of the upper urinary tract: Review of initial experience ex vivo and in vivo

Diagnostic imaging of the upper urinary tract is a cumbersome process that involves a multitude of different imaging modalities, including ultrasonography, conventional radiography, X-ray fluoroscopy (retrograde and antegrade ureteropyelography), endoscopy (cystoscopy and ureterorenoscopy) without or with biopsy, multi-detector-row computed tomography (MDCT), and magnetic resonance imaging (MRI). However, these modalities leave a diagnostic gap because they cannot demonstrate different layers of the wall of the upper urinary tract. Recent research shows that catheter-based, intraluminal probes for optical coherence tomography (OCT) with near-infrared light provide cross-sectional images from within the lumen of the upper urinary tract that distinguish between the urothelium, lamina propria, and muscle layer at spatial resolutions of about 10–15μm in axial and about 20–25μm in lateral directions respectively. The feasibility of in vivo imaging and the superiority of OCT to endoluminal ultrasonography (ELUS) have been demonstrated. However, OCT has yet to show that it is capable of characterizing pathologic lesions, e.g., urothelial cancer. The present paper summarizes the basic principles and initial results of catheter-based, time-domain intraluminal OCT in the upper urinary tract.